Your supposition that the translation would be
Las manzanas no le gusta a Sonia
is almost correct. With the apples being the subject, the verb simply needs to agree to be perfectly cromulent.
Las manzanas no le gustan a Sonia
Word order in Spanish is more flexible than in English and importantly, word order does not define the roles that words have in the sentence. The sentence "Sonia likes apples" can be translated six different ways in Spanish:
SVO: Las manzanas no le gustan a Sonia. SOV: Las manzanas a Sonia no le gustan. VOS: No le gustan a Sonia las manzanas. VSO: No le gustan las manzanas a Sonia. OSV: A Sonia las manzanas no le gustan. OVS: A Sonia no le gustan las manzanas.
All mean the exact same thing, but there can be difference in emphasis. To respond to a question about if Sonia likes/dislikes something, and you want to clarify it's actually apples that she doesn't like, you'd probably go with a SVO/SOV option. If someone suggests having apples, you'll probably go with a VOS/VSO option. If someone wonders who doesn't like apples, you'll go with a OSV/OVS. The OVS is the most common, and most neutral in interpretation.
In English you can kind of mimic this type of emphasis by actually pronouncing a word longer/louder: